<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>概述</title>
</head>

<body>
    <button onclick="alert('大家好')"></button>
    <a href="javascript:;" onclick="alert('very good')">单击</a>
    <a href="javascript;alert('good')">单击</a>
</body>

</html>
<script>

</script>